In this project, I will ask whether there are neuronal cell surface molecules that share a common protein backbone, but display structural variations from neuron to neuron. Such molecules may well be involved in defining neuronal specificity. My approach will be to use monoclonal antibodies as monospecific reagents, and different human neuroblastoma-derived cell lines as sources of homogeneous material. The basic sequence of experiments will be: (1) To develop a panel of monospecific antibodies, each of which recognizes several different neuroblastoma-derived lines as well as normal nervous tissue, (2) to use each antibody to immunoprecipitate its antigen from the surface of two or more of the cell lines, (3) to use SDS-PAGE, IEF and peptide map analyses to ask whether any of the molecules show structural microheterogeneity from cell line to cell line. In carrying out this project, I will of necessity be characterizing those molecules that are present on human neuroblastoma-derived cell lines and are also shared by normal nervous tissue. Thus, I will be starting to form an immunological and biochemical map of the normal human neuron.